The present invention relates to a hydraulic cylinder and to a clamp device, and in particular relates to a technique for providing a detection mechanism with which the position of a piston member that is a object of detection can be freely set, with the detection mechanism having a compact structure.
In the prior art, a hydraulic cylinder that is employed in a clamp device that clamps an object for clamping such as a workpiece or the like which is to be supplied to machining has comprised a cylinder main body, a piston member that is provided in the cylinder main body so as to move freely forward and backward therein, a hydraulic pressure operation chamber for driving the piston member in at least one of its advance direction and its retraction direction. In such a hydraulic cylinder, various rod position detection techniques have been implemented for detecting a forward limit position of the piston member of the hydraulic cylinder in its axial direction, and a backward limit position thereof, an intermediate limit position and so on.
For example, in the hydraulic cylinder of JP Laid-Open Utility Model Publication Showa 55-84301, a reciprocating type piston is received in a cylinder bore within a cylinder main body, auxiliary chambers and detection pistons are provided in the end walls at each end of the cylinder main body, and, when the piston arrives at an end of its stroke, along with the corresponding detection piston being pushed toward the exterior by the piston and the piston being slowly stopped via the detection piston and via a fluid passage that is formed therein, also the fact that the piston has arrived at the end of its stroke is detected by an external limit switch for detecting the end of the stroke.
And, in the clamp device of JP Laid-Open Patent Publication 2001-87991 that includes a hydraulic cylinder, the position of the piston rod (i.e. the end of its stroke) is detected by a pressure sensor that detects the hydraulic pressure supplied to the hydraulic cylinder, and by a two-position sensor that detects an upper position and a lower position of a portion to be detected at the lower end portion of an operating rod that projects to the exterior from the piston member of the hydraulic cylinder.